Cap Fungi – Mushrooms and Toadstools

Technical Update

Autumn is often referred to as the ‘season of mists and mellow fruitfulness’ and each year it can bring back the problems caused by fungi on turf.  Falling night temperatures cool the soil, thus slowing the growth of grass and, with an increase in humidity that results from frequent autumn rainfall, conditions are right for the invasion of the fungi.  Greenkeepers and groundsmen get ready to do battle with the disease patches that can spoil the appearance and play of the turf they manage.  However, this is also a time when we see an invasion of the macroscopic fungi that also inhabit the soil.  These cap producing fungi literally give ‘rise’ to the structures we know as mushrooms and toadstools. In this short article I will be taking a look at the larger fungi and the options we have to deal with them.

According to literature there is no difference between mushrooms and toadstools; except perhaps on the weekly shopping list, where most supermarkets offer only a variety of different mushrooms for sale!  The terms mushroom and toadstool both refer to the fruiting body of types of fungi that produce these large structures, whose sole purpose is to distribute reproductive spores.  In the past there was a tendency to refer to poisonous species as toadstools but there was no clear rule on this.  Many thousands of species of mushrooms are found worldwide; a rough estimate would be 20,000 species globally with some 4,000 in the UK.  Mushrooms are classified in the order Agaricales and are spread between two phyla; Basidiomycota and Ascomycota.  The ‘white’ or ‘button’ mushroom (Agaricus bisporus) is the most common form of edible mushroom, accounting for 90% of all types consumed in the western world.  Some strains of A. bisporus have darker flesh and are sold as ‘Portobello’ and ‘chestnut’ mushrooms.

Certain species of mushrooms are highly nutritious; providing us with a balanced food that is low in fat, carbohydrates and salt yet contains some essential minerals and vitamins.  Healers in ancient times recognised the medicinal benefits of mushrooms and today our scientists have discovered the valuable contribution they make towards improving well-being; lowering cholesterol, blood pressure, supporting the immune system and helping in the fight against certain forms of cancer.

The vast majority of mushrooms are edible although not all will suit the human palate.  A few species are poisonous and can have serious or even fatal consequences when consumed.  Some poisonous mushrooms appear similar to edible varieties, so extreme caution must be exercised when eating wild mushrooms. The land owner’s permission should also be sought before picking fungi.

There are three types of problems caused by macroscopic fungi on turf.  

  • Litter left behind when the fruiting structures are broken up by mowing.
  • Fairy rings
  • Hallucinogenic species

A cluster of bonnet mushrooms on a lawn

The presence of mushrooms littering the surface can usually be attributed to pieces of decaying wood or dead plant matter below the surface.  The fungus is just doing a bit of re-cycling and will not damage the grass other than making a mess.  There are no chemical remedies to deal with this problem so probably the easiest method of control is to remove the caps as soon as possible after they are first seen.  Grasp the stalk as low down as possible and deposit the caps well away from the turf – on a compost heap would be best.  

Mushroom gills bear reproductive spores

The reproductive spores are often borne on gills on the underside of the cap.  When mature they fall and are carried on the wind to establish the mushroom in new locations.  If the caps are removed cleanly and swiftly we can hope to minimise the spread of the problem in future.  I have noticed that the caps on my lawn wither when I apply an autumn fertiliser, which may be due to the high iron content in the product.

The second group of problem mushrooms on turf are produced by fairy ring fungi.  Strictly speaking they cause a disease of the soil rather than the turf because there is no invasion of the grass plant tissue.  Instead we see symptoms that are external effects on the turf caused by a fungal presence beneath.  The fungal mycelium is usually found between 75 and 150mm below the grass surface.  The ring shape is the result of the underground fungal mycelium growing in a rough circle away from a starting point.  The rings will increase in size each year as the fungus moves through the soil, feeding on organic matter as it spreads outwards.  Depending on the species, the ring will increase in diameter by 30 to 50cm per year.  If you are prepared to wait long enough it will eventually move into neighbouring land!  If two rings meet they usually join together as one.  We recognise three types of fairy ring according to the severity of the symptoms. 

Type 1 fairy rings produce a circle in which the grass is stunted or absent.  There are usually toadstools arising from this area of poor growth (dead area) and for a few cm on either side.  The dead area is caused by the deposition of thick wax in the soil where the fungus is located, which prevents water from reaching the grass roots.

Cross section through a type 1 fairy ring

Type 1 rings are also characterised by a band of stimulated grass adjacent to the dead area; which is longer, thicker and darker green in colour when compared to the surrounding turf.  The stimulated growth results from excretion of waste products such as nitrates and other nutrients by the fungal mycelium as it breaks down organic matter for food.  

Type 1 fairy ring cap